I have been looking (for years) for a "good" online storage/sync solution that allows me to store my documents using my own private key. TrueCrypt etc don't reach the "set it, and forget it" level.
But when you think about how much more expensive storing those documents will be for these companies (as each copy of the same document will be encrypted with a separate private key), and how much value these companies will miss out on because they won't be able to scan our documents, it's understandable why I may never find such a solution.
Provides a pain-free encrypted layer on top of free cloud storage services like DropBox. BoxCryptor encrypts individual files, then stores the encrypted files in DropBox. If your DropBox account is compromised the adversary will only get useless encrypted files. Uses EncFS. Has clients for Windows and Mac. The Android and iOS clients are amazing.
To me, the most surprising thing about BoxCryptor is that it's easier to use than DropBox--not an easy feat.
Pretty much ANY online service that provides sync has decided not to use private keys. The same goes also with tasklist apps. They are either only web-based (and obviously readable at the server) or use the sync without encryption to provide web access. http://timegt.com is using private key for encrypting sync data but it came with the cost of not having any web access to your tasks!
The same with dropbox etc, private key encryption renders any server-side magic like web access very complex.
Not sure if it's exactly what you're looking for but you could consider tarsnap.com, which is an online storage company heavily focused on user security/privacy. It's been around for many years now and is run by HN's cperciva (IIRC), who seems to be quite knowledgeable with all things security.
And if someone were working on this (or hoping to) how could they reach you to let you know about a beta/alpha? (genuine question, I've been thinking about something similar).
But when you think about how much more expensive storing those documents will be for these companies (as each copy of the same document will be encrypted with a separate private key), and how much value these companies will miss out on because they won't be able to scan our documents, it's understandable why I may never find such a solution.